The present invention relates to pigment dispersions containing a viscosity-reducing additive. By lowering the viscosity of the dispersions, still more pigment may be added to the dispersions, resulting in a very highly concentrated dispersion which can be satisfactorily handled and dispersed.
Pigments sold to ink manufaturers are usually in two forms: (1) dry powders and (2) concentrated dispersions. Pigments sold in the second form are offered at as high a concentration as the ink manufacturer can use, in order to provide the following advantages to the ink manufacturer:
(A) a more concentrated pigment dispersion allows the inkmaker greater formulating latitude (e.g. to increase performance or lower costs) because less dispersion must be added to maintain any particular pigment level in the ink; and PA0 (B) the greater formulating latitude permits the inkmaker to produce a wider variety of inks (e.g. the same dispersion could go into heatset, quick-set, and news ink); PA0 (C) the more concentrated pigment dispersion permits a lower inventory volume and less raw material testing by the inkmaker. PA0 (1) an oil-soluble, long-chain aliphatic amine having a molecular weight between 80 and 340, with PA0 (2) a polybasic organic acid having a molecular weight between 50 and 250. PA0 (1) dissolving x moles of the amine in an aliphatic solvent, in order to form an amine solution; and PA0 (2) heating the amine solution to approximately 90.degree. C., accompanied by mild agitation; and PA0 (3) discontinuing heating and simultaneously adding x moles of the acid, followed by mixing the acid with the amine solution for about 15 minutes while the amine solution is cooling, followed by allowing the resulting mixture to cool to room temperature.
The upper limits of pigmnt concentration are determined by physical handleability. As the pigment concentration in the dispersion increases linearly, the viscosity of the dispersion increases exponentially. If the dispersion is too high in viscosity, the inkmaker can no longer satisfactorily disperse the concentrated pigment in the ink manufacturing process. Furthermore, as the pigment concentration increases, the ink manufacturer experiences increasing frictional heat buildup during the dispersion process. This heat buildup will degrade certain pigments. In addition, as the inkmaker's dispersion difficulties increase, so does the amount of labor-intensive handling required to achieve successful dispersion.
Most pigment dispersion manufacturers operate near an upper limit of pigment concentration, in order to provide inkmakers with the several adantages described above, without creating the problems resulting from too high a pigment concentration. The product and method of the present invention enable the manufacturer of a pigment dispersion to significantly decreae the viscosity of a pigment disperion by adding a relatively small amount of a viscosity-reducing agent. The lower viscosity allows the pigment dispersion manufacturer, in turn, to increase the pigment concentration back to the point at which the resulting maximum viscosity is reached. Thus the pigment dispersion manufacturer may now produce a dispersion which has a viscosity at the maximum amount and pigment concentration significantly above the concentration attainable without use of the additive.
The closest art of which applicants are aware is PCT application WO 84/02142, published 7 June 1984, to Inmont Corporation. This application discloses the use of a water-soluble buffer for use in lithographic fountain solutions in which the buffer is a salt of a polycarboxylic acid and an organic amine. The present invention differs from the Inmont application in that the Inmont application nowhere suggests the addition of an oil-soluble buffer to a flush. In order to produce the desired result of the present invention, the additive must be added to an oil-based flush, rather than to the water-based fountain solution referred to in the Inmont application. Thus both the purposes and means of the present invention are different from the Inmont application.